GST Calculator
Add or remove GST from a price.
GST Calculator at a glance
GST Calculator is a free online calculator you can use right now to add or remove GST from a price โ no account, no install and no usage limit. It runs entirely inside your browser, so whatever you enter stays on your own device.
- Price
- Free โ no trial, no paid tier, no watermark
- Sign-up
- Not required
- Where it runs
- In your browser โ nothing is uploaded to a server
- Works on
- Chrome, Safari, Firefox and Edge โ desktop, tablet and phone
- Category
- Calculators
About GST Calculator
Add GST to a price that excludes it, or work backwards to find the tax already contained in a GST-inclusive price.
The reverse calculation is where errors happen. To remove GST from an inclusive price you divide rather than subtract the percentage. At 18%, an inclusive price of 118 contains 18 of tax โ but subtracting 18% of 118 gives 21.24, which is wrong. The correct method is to divide by 1.18, giving a net price of 100 and tax of 18. Subtracting the percentage from the gross figure always overstates the tax.
This matters commercially because invoices must state the net amount, the tax and the gross separately. Getting the reverse calculation wrong means the three figures do not reconcile, which causes problems at filing time and in any audit.
The correct treatment depends on registration and location. Whether you must charge GST or VAT at all, at what rate, and whether a reverse-charge applies to a client in another jurisdiction are questions with country-specific answers that also depend on your registration status. This tool does the arithmetic; which rate applies to a given transaction is worth confirming once with an accountant and then applying consistently.
How to use GST Calculator
- Enter the price and choose whether it currently includes GST.
- Set the applicable GST rate.
- Read the net amount, the tax and the gross total.
Frequently asked questions
How do I remove GST from an inclusive price?
Divide, do not subtract. At 18%, divide the gross by 1.18 to get the net. Subtracting 18% from the gross price overstates the tax and gives the wrong net figure.
Why does subtracting the percentage give a different answer?
Because the percentage was applied to the smaller net figure, not the larger gross one. Taking 18% of the gross removes more than was originally added, which is why division is the correct reverse operation.
Which rate applies to my sale?
That depends on your country, the goods or services involved and your registration status. Cross-border transactions often involve reverse-charge rules. Confirm the correct treatment for your situation with an accountant.
Do I show GST separately on an invoice?
Generally yes โ most tax regimes require the net amount, the tax amount and the rate to be stated separately from the total. This is also why the reverse calculation must be exact.